Conrad-
The only thing I would add is to use a heavy duty swivel between the pull
rope and the bundle of cables you're pulling, to further minimize twisting
inside the conduit.
73,
Steve
N6SJ
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Grant
Saviers
Sent: Wednesday, March 05, 2014 8:54 AM
To: conrad@g0ruz.com; towertalk@contesting.com
Subject: Re: [TowerTalk] Installing/burying LDF5-50A
Conrad,
Not sure what you have locally, probably something similar in metric or
still Imperial in the construction trades -
IMO, regular sch40 PVC conduit is the best choice for moisture, critter and
crush resistance. Use 3" or 4" diameter and the large radius (min 36"
radius) sweeps (90 degree bends). 3" will hold 3 x LDF5 plus
control wires if pulled together with liberal amounts of pulling lube.
I recently recovered a dozen runs of LDF5 from several 3" x 140'
conduits and it removed easily as the condensation inside the buried
conduit kept the 8 year old lube slippery. For both ends, buy a large
fiberglass enclosure (24 x 36 x 12" or larger) and put your grounding plate
in it with RG jumpers into the shack from there. Or use 90 degree
connectors if LDF has to go into the shack for some reason. The station I
recently took apart was all 7/16 DINs to a 2' x 3' Cu shack end ground plate
with 20 bulkhead through F-F DINs soldered to it - very first
class! I mounted my enclosures so the tower run conduits enter at the
bottom and the two through wall 3" conduits for RG jumpers into the shack go
out the back. For 4 towers you will probably need more than one enclosure
at the shack end. Similarly at the tower end the enclosure with the bottom
of the tower grounding plate holds the lightning arrestors and transitions
to the coax runs up the tower,
whatever they are. The tower runs go through holes in the cabinet
bottom so there a drip loop. The cabinet is also a good place for
stack switches.
Glue all the conduit together and bury it before pulling wires. If the soil
has sharp rocks, some "5/8" and down" gravel bedding and cover will protect
the PVC from being punctured. Sand is often the code standard, but it
washes out easily if there is an opportunity for that. Conduit measuring
tape is a good way to run a messenger line, tied to a crumpled up plastic
bag and sucked through with a shop vac. Then you will know the exact length
for the LDF. I've been surprised when the calculated length was shorter
than the measured length and cables were cut - oops!
Run extra cables for the future (mine are CAT5, RG6, 8 wire 18ga control, 1x
Buryflex RG8), since as others have pointed out, it's very difficult to pull
a new cable in conduit with existing cables, but leave
a couple of measuring tape lines "just in case". A 3000' spool of
measuring tape costs about $80. btw, use braided rope or the flat webbing
made for wire pulling as the pull rope, not 3 strand rope since it will
cause twist in the cables.
It takes a pressurized dry air or nitrogen system to keep condensation out
of buried conduit, so plan to use control and power wires rated for burial.
Some are flooded with silicone grease to prevent moisture wicking if the
cover is nicked.
Grant KZ1W
On 3/4/2014 9:34 AM, Conrad Farlow wrote:
> My radio club will shortly have 4 towers and I would like to run
> lengths of LDF5-50A to the base of the tower from the shack. The
> lengths are not particularly long but I would like to bury them to
> keep them neat. I have very little idea of how to do this properly, in
> particular how to put a correct bend into the cable where it leaves
> the ground pipe and enters the shack. Does anyone have any photos'
> guidance on how they have done this?
>
> I am assuming that the cable should be put inside some large diameter
> plastic pipe that has a good number of pull ropes installed prior to
> burying them.
>
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